Cellular telephone service in the United States is provided by numerous companies which provide service in separate geographical regions. The Federal Communications Commission (FCC) has licensed two cellular carriers in each Metropolitan Service Area (MSA) and Rural Service Area (RSA), of which there are 306 and 428, respectively. The service area within each individual region is divided into many distinct sub-regions, commonly referred to as cells.
Each cell within a region contains a single cell-site control system (CSC), which is composed of a processor, one or more radio receiver/transmitters, and one or more radio antennas. The CSCs in a region are connected to a network control system (NCS), which controls all cellular telephone connections within that region. The NCS is, in turn, connected to one or more wireline telephone company central offices (COs) in the region.
Each CSC is responsible for all customers having a cellular telephone presently located in the corresponding cell. In particular, when a cellular telephone is turned on, it may transmit a signal indicating that it is ready to place and/or receive calls. This signal is received by CSCs in the immediate area. The received signals are then fed to the NCS. The CSC that receives the signal the strongest is generally the CSC that is contained in the cell in which the cellular telephone is located. As such, the NCS makes the particular CSC responsible for supporting calls involving that cellular telephone.
If a call is placed or received by that telephone, the NCS transmits the voice signals, as well as the data signals necessary for setting up and controlling the voice signals, to the responsible CSC. The CSC sends a data message to the mobile telephone, assigning that telephone an unoccupied pair of frequencies in which signals are to be transmitted and received (the transmitting frequency being different than the receiving frequency). Thereafter, all of the signals transmitted during the cellular phone call are handled by the responsible CSC on the assigned frequencies.
If, during a conversation, the cellular telephone, which may be located in an automobile, for example, moves from one cell to another, signals may be received stronger by the CSC in the new cell, in which case, the NCS may make the CSC in the new cell responsible for that cellular telephone, and the call in progress is handed-off to the new cell.
However, because different companies provide cellular telephone service to the various regions throughout the United States, complications may arise when a customer of a first company which services a first (home) region is located in a second (foreign) region serviced by a second company ("roaming"). Some cellular carriers have entered into roaming agreements pursuant to which they will provide service to each other's subscribers. Indeed, the NCSs of the regions may, but need not, be connected to support such conversations. As such, placing a call by a customer in a foreign region may be as simple as dialing the area code and number. Calls originated by the roaming subscriber are handled by the foreign systems, and applicable charges are billed to the subscriber's home system operator. Substantial premiums may apply to calls originated by roaming subscribers.
However, problems arise in locating a customer in a foreign region (serviced by a different company) so that calls can be received by the customer. In a cellular telephone system having a "Standard Roaming" feature, a party desiring to reach a customer in a foreign region must know the particular foreign region in which the customer is located, which of the two systems in the foreign region is providing service to the roaming cellular telephone, and the access number of the NCS of the service providing system in the foreign region. The party must then dial the access number followed by the area code and local number in order to call the customer.
In a cellular system having a "Follow Me Roaming".RTM. feature (registered trademark of GTE Mobilnet), once a customer enters a foreign region, he may press particular buttons on his cellular telephone in order to activate Follow Me Roaming, i.e., he may transmit a signal to the nearest CSC in order to notify the NCS in the foreign region and, in turn, the NCS in the home region that he is presently located in the foreign region. A party desiring to call the customer would then need to dial only the area code and local number, because the home NCS knows to which foreign NCS to route the call, i.e., the home NCS knows in which foreign region the customer is located.
The customer must activate Follow Me Roaming in each new region into which the customer travels by pressing the particular buttons on the cellular phone. Inconvenience to the cellular telephone user arises because (a) the subscriber must first know that he/she has, in fact, entered into a foreign cellular service area, (b) the subscriber must manually activate the Follow Me Roaming feature, and (c) when on an extended journey which traverses many foreign cellular service areas, the subscriber must continually be aware of his/her entering into a new area and must activate the Follow Me Roaming feature again and again. Deactivation of Follow Me Roaming is achieved by pressing other buttons on the cellular phone.
To eliminate this inconvenience on the customer, it is also known for a cellular telephone to provide identification information (i.e., the I.D. of the unit's home NCS) automatically, immediately after being turned on in a foreign region. As in systems having Follow Me Roaming, the foreign NCS then notifies the home NCS of the whereabouts of the customer, allowing callers to dial only the local telephone number in order to reach the customer. However, such a feature is not available in many regions of the United States.
Moreover, when a call is forwarded to a cellular telephone subscriber in a foreign region, the subscriber is charged for the air time and for the long distance portion of the call, even if the subscriber receives an unwanted ("nuisance") call.